MISCELLANEOUS OBSERVATIONS. 



I. A REPORT ON THE GROUND CURRENT OBSERVATIONS MADE AT UGLAAMIE, 



ALASKA. 



By A. L. McRAE, Pr irate Signal Corps, U. S. Army. 



The observations were commenced August 11, 1882, and were continued at hourly intervals 

 until November 14, 1882. 



The lines were insulated wires one thousand yards in length. One was in the magnetic 

 meridian, and the other at right angles to it. 



The terminals were copper plates 2 (1?) feet square. The N., S. and W. terminals were in water; 

 the E. in laud. 



Compass galvauoscopes were used to measure the strength of the current. 



As the observations possess especial interest because they were made in such a high latitude, 

 several deflections of the galvanoscope have been reduced to something like absolute measure by 

 comparison with a galvanometer in the laboratory. 



Unfortunately the electromotive force due to the terminals and the resistance of the complete 

 circuit were not determined, so that their effects cannot be accurately estimated. 



But from an experiment with copper plates one, square toot in area it was found that the 

 electromotive force under the most favorable circumstances, when both plates were in sea is less 

 than .05 volt, and when one plate was in sea and the other in land is less than .2 volt. 



Mr. Wild has found that the electromotive force due to copper plates buried in the earth may 

 reach .05 volt. We can therefore safely assume that the electromotive force between the plates 

 used in the observations was not greater than .2 volts. 



Mr. Wild has already found that the resistance of the ground between copper plates one 

 square meter in area buried two meters below the surface and one kilometer apart was between 

 thirty and sixty ohms. By comparison the resistance of the ground at Uglaamie would be between 

 eighty and one hundred and sixty ohms. But since all the plates except one were in water it is 

 probable the resistance was much less. 



If we assume that the resistance of the line and the ground was so small compared to the 

 resistance of the galvanoscope as to be inappreciable, we find that at times there was an electro- 

 motive force of .8 volt acting. Deducting the .2 due to the terminals we have . volt remaining, 

 which must be due to a ground current. 



The difficulties mentioned above of eliminating everything from the true ground current 

 prevent a careful study of the observations; but by plotting the total current it appears that: 



1. The current is generally steady in strength and direction for several days at a time. There 

 are periods when there is no current. *Tliere are also rare moments when the intensity of the 

 current changes rapidly. The direction of the enrreiit usually changes slowly. 



2. The north and south component is the stronger. 



3. The general direction of the current is from the first (NW.) to the third (SE.) quadrant, 

 and not from the second (NE.) to the fourth (SW.) as in Europe. 



The general direction varied from due west to a little east of north. 



In connection with auroras it is noticed that: 



On September 4 a weak variable current suddenly changed to a strong north by east enrrrent 

 six or seven hours before an aurora was observed. This strung current continued for several dajs 

 and auroras on the Gth, 12th, and 15th did not seem to afl'ect its intensity or direction. 



